import React, { Component } from 'react'

export default class Count extends Component {
  state={
    count:0
  }
  increment =()=>{
    this.setState({count:this.state.count+this.selectNum.value*1})

  }
  decrement =()=>{
    this.setState({count:this.state.count-this.selectNum.value})

  }
  incrementIfOdd =()=>{
    const count = this.state.count
    if(count%2!==0){
      this.setState({count:count+this.selectNum.value*1})
    }
  }
  incrementAsync =()=>{
    setTimeout(() => {
      this.setState({count:this.state.count+this.selectNum.value*1})
    }, 800);
  }
  render() {
    return (
      <div>
        <h1>当前求和为：{this.state.count}</h1>
        <select ref={c=>this.selectNum=c}>
          <option value="1">1</option>
          <option value="2">2</option>
          <option value="3">3</option>
        </select>
        &nbsp;
        <button onClick={this.increment}>+</button> &nbsp;
        <button onClick={this.decrement}>-</button> &nbsp;
        <button onClick={this.incrementIfOdd}>当前和为奇数+</button> &nbsp;
        <button onClick={this.incrementAsync}>异步+</button>
      </div>
    )
  }
}
